In each of vehicles such as an electric-powered car and a hybrid car, a power battery or an auxiliary battery is mounted. As this kind of battery, there is often used a so-called assembled battery in which many storage batteries are connected in series.
Further; each of some vehicles has a charger which is used for charging a battery mounted therein. The charger converts a commercial power source of 100 V or 200 V into a predetermined voltage and supplies the converted voltage to a battery, whereby the battery is charged.
When this charger is used to charge the assembled battery, as shown in FIG. 9, a predetermined voltage is applied to the entire assembled battery 200 to perform charging (see, e.g., Patent Literature 1).
Specifically, for example, a charger 110 for 140 V is connected to the assembled battery 200 in which 10 storage batteries BTT of 14 V are coupled, whereby the charging is performed.
However, when the assembled battery is charged in such a configuration, a considerable time is required until completion. For example, as shown in FIG. 10, when a substantially fixed amount of charging voltage is continuously supplied, a long charging time of approximately eight hours is required. In this case, a user has to wait for eight hours until the next driving, which is not practical.
Therefore, technologies that shorten the charging time have been suggested. For example, there has been suggested a technology for intermittently controlling supply and stop of a charging current to allow the charging current to flow in a pulsed manner. (see, e.g., Patent Literature 2).
When the pulse charging is performed as in the case of this technology, the charging time can be shortened as compared with a situation where a fixed amount of charging voltage is supplied.